Feng Xu

During the formation and triggering process of reservoir-induced seismicity (RIS), rock mass conditions, load conditions, and water occurrence conditions all have a significant impact. As the mechanism of RIS is the core and difficult problem in RIS measurement research, and the mechanism model of quantifiable calculation and analysis at any point of reservoir influence area is lacking, the additional stress model suitable for any location of reservoir were proposed and established in this paper. Based on the model, complete calculation of additional stress in reservoir space is realized, the distribution of additional stress on the reservoir section is obtained, and the influence of reservoir shape and size on the additional stress is discussed. The additional stress model of water level fluctuation considering the influence of water storage and drainage is established, then, the distribution of additional stress and the influence of water level fluctuation on induced seismic are analyzed, and a more simplified and general theory of additional stress coefficients is established. The results show that the variation of water level has a significant effect on the additional stress, and the increase of water level will lead to the increase of additional stress.

Hydrogen (H₂) sensors are critical to various applications such as the situation where H₂ is used as the clean energy for industry or the indicator for human disease diagnosis. Palladium (Pd) is widely used as the hydrogen sensing material in different types of sensors. Optical fiber H₂ sensors are particularly promising due to their compactness and spark-free operation. Here, we report a Fabry–Pérot (FP)-cavity-based H₂ sensor that is formed with a freestanding Pd membrane and integrated on a conventional single-mode optical fiber end. The freestanding Pd membrane acts both as the active hydrogen sensing material and as one of the reflective mirrors of the cavity. When the Pd film absorbs H₂ to form PdH_x, it will be stretched, resulting in a change of the cavity length and thus a shift of the interference spectrum. The H₂ concentration can be derived from the amplitude of the wavelength shift. Experimental results showed that H₂ sensors based on suspended Pd membranes can achieve a detection sensitivity of about 3.6 pm/ppm and a detection limit of about 3.3 ppm. This highly sensitive detection scheme is expected to find applications for sensing low-concentration H₂.

Reliable gas sensors are very important for hydrogen (H₂) gas detection and storage. Detection methods based on palladium (Pd) metal are cost-effective and widely studied. When Pd is exposed to H₂, it turns into palladium hydride with modified optical properties, which thus can be monitored for H₂ sensing. Here, we fabricated large-area Pd nanostructures, including Pd nanotriangles and nanohole arrays, using colloidal lithography and systematically studied their H₂-sensing performance. After hydrogen absorption, both the Pd nanoholes and nanotriangles showed clear transmittance changes in the visible–near infrared range, consistent with numerical simulation results. The influences of the structural parameters (period of the array P and diameter of the nanohole D) of the two structures are further studied, as different structural parameters can affect the hydrogen detection effect of the two structures. The nanohole arrays exhibited bigger transmittance changes than the nanotriangle arrays.